A solar hot water system uses heat from the sun to heat water. In a typical system, a solar collector is placed on a roof to absorb solar heat. The collector heats fluid that is either pumped or driven by convection through it. The heat from the collector is stored in a hot water storage tank. There is a separate loop of fluid containing anti-freeze that delivers heat to the tank through a heat exchanger.
System Description:
Materials Used:
The primary component of the system, the collector, is made of a glass-top insulated box with a solar absorber made from sheet metal. This is attached to copper heat exchanger pipes.
Direct vs. Indirect Systems:
A direct system is an open loop system that circulates potable water through the collectors. Indirect systems are closed loop systems that use heat exchangers that separate potable water from the fluid. The heat exchanger transfers heat from the heat transfer fluid to the potable water. Indirect systems are safer because they have freeze protection and overheat protection, where a direct system does not. Both sysems are shown in the diagrams above. The main difference is that the indirect system is more complex-having a heat exchanger and sensors.
Passive vs. Active Systems:
The diagrams above comparae passive and active solar hot water systems. When the fluid is pumped, it is an active system. When the fluid is driven by natural convection, it is a passive system. Passive systems are less expensive and low maintenance. However, overheating and freezing are major concerns because drainback systems can’t be used. A passive system is a lot less efficient. Active systems are not only efficient; they allow for increased control of the system, freedom in design, and can have drainback tanks. The heat loss through the system is low in an active system, because the storage tank can be placed in conditioned spaces. Even though it is safer and more efficient than a passive system, an active system is more expensive.
Indirect System
Direct System
